I'm trying to lose weight, and I have some questions... to clarify some of the weight loss tips that the Internet gives us.

1. I know you're supposed to not weigh yourself throughout the day, but I do, just to see how my weight fluctuates. Sometimes after a meal or drinking water, my weight will jump up 2-3 lbs. How do you know if you're eating too much, or if the weight gain is just caused by water retention or pre-bowel movement?

2. I read somewhere that you shouldn't eat after 7pm, because your metabolism slows down before bed. Is this true?

3. How does metabolism work throughout the day? I've heard that if you eat breakfast, it jump-starts your metabolism. I've also heard that you should eat smaller meals spread out throughout the day to keep your metabolism going. But how do you know it's all working?

I would not weigh myself multiple times through out the day. Maybe once in the morning at the same time every day.
Eating after seven.....well I think a lot of that is that your activity level is lower than throughout the day. Always best not to eat three hours before bed.

I get my energy by lifting weights and circuit training every morning. It is a natural energy for me.

Fluid retention is just that. It has no bearing on fat loss, which is what you're aiming for. Weighing multiple times is informative in that it tells you how your weight fluctuates throughout the day, but does not tell you how your weight loss program is progressing. If fluctuations are going to bother you then you're better off to set one day a week to weigh, first thing in the morning before any food or drink, with the least amount of clothing.

It is a personal decision to eat 3 meals a day or more frequent smaller meals. Try different ways and see what works best for you. Eating too close to bedtime disrupts your sleep because your body is digesting food when it should be resting and repairing. At the same time, if you go to bed really hungry it might also interfere with your sleep. If anything, have a small healthy snack. The same with exercising too close to bedtime. A good nights sleep is important for weight loss.

Are you tracking your food? That will help you determine if you are eating too much. If your weight loss stalls, look at your recent meal entries and see where you can make cuts or changes. Some stalls are normal, as you lose, your body adjusts to the weight loss. Just when you think you can't lose any more, you will drop some more weight.